Search results for "Electron ionization"
showing 10 items of 82 documents
Cross-sections for (e, 3e) collisions on helium: the DS6C wavefunction
2006
A dynamically screened product of six pairwise Coulomb functions (DS6C) is used as an analytic approximation to describe the four-body Coulomb continuum state produced by electron-impact full fragmentation of helium. Good agreement is obtained with experimental data close to threshold, where four-body effects are expected to be important. Even for the high impact energy of 640 eV, four-body effects still play a role in deciding the shape of multi-differential cross-sections.
The effect of dynamical screening on helium (e, 3e) differential cross-sections
2005
A simplified derivation of dynamic screening in the case of three Coulomb-interacting particles in the continuum is given and applied to describe the shapes of multi-differential cross-sections for the (e, 3e) process on the helium atom in which the incident fast electron is treated in first-order Born approximation. A very good agreement with experimental multi-differential cross-sections is obtained for two slow ejected electrons (specifically both electrons have 5 eV) but the strategy appears to be breaking down at intermediate emission energies.
A study of VUV emission and the extracted electron-ion ratio in hydrogen and deuterium plasmas of a filament-driven H−/D− ion source
2019
Vacuum ultraviolet (VUV) emission diagnostics for studying differences of electron impact processes in hydrogen and deuterium plasmas are presented. The method is applied to study a filament driven multicusp arc discharge negative ion source by comparing the VUV-emission intensities of different emission bands and extracted currents of H−/D− ions and electrons. It was found that the ratio of coextracted electrons to extracted ions is four times higher for deuterium than for hydrogen. No significant differences of the VUV-spectra or volumetric rates of ionization, excitation, production of high vibrational states, and dissociation were found between the plasmas of the two isotopes. The volum…
Resonant three-photon ionization spectroscopy of atomic Fe
2013
Laser spectroscopic investigations on high-lying states around the ionization potential (IP) in the atomic spectrum of Fe have been carried out for the development of a practical three-step resonance ionization scheme accessible by Ti: sapphire lasers. A hot cavity laser ion source, typically used at on-line radioactive ion beam production facilities, was employed in this work. Ionization schemes employing high-lying Rydberg and autoionizing states populated by three-photon excitations were established. Five new Rydberg and autoionizing Rydberg series converging to the ground and to the first four excited states of Fe II are reported. Analyses of the Rydberg series yield the value 63 737.68…
Experimental investigation of electron impact onSi2−
2008
A merged beams technique has been used to investigate collisions between electrons and $\text{Si}_{2}{}^{\ensuremath{-}}$ ions over a relative kinetic energy range of 0--210 eV. Absolute cross sections for pure electron detachment, detachment plus dissociation, and dissociation involving atomic and ionic products were measured. The dominant process over the energy range studied is pure electron detachment. A search for a resonance associated with a ${\text{Si}}_{2}$ dianion was made but none was observed.
Nonlinear collective oscillations of an ion cloud in a Paul trap
1997
In an experiment using a Paul trap, we create a ${\mathrm{H}}_{2}^{+}$ ion cloud by electron ionization of the background gas at ${10}^{\ensuremath{-}9}$-mbar residual pressure. Exciting the ions parametrically at twice the frequency of the secular motion of ions in the $r$ or $z$ direction, we observe a narrow resonance at some distance from the motional resonance center if the amplitude of the exciting field exceeds a threshold value. The threshold value decreases with increasing ion number. Since the narrow resonance does not shift with ion number, we interpret it as a collective resonance of the center of mass of the ion cloud. The resonance shape exhibits the typical form of a driven a…
Three-photon resonance ionization of atomic Mn in a hot-cavity laser ion source using Ti:sapphire lasers
2015
Three-photon resonance ionization of atomic manganese (Mn) in a hot-cavity ion source using Ti:sapphire lasers has been demonstrated. Three-step ionization schemes employing different intermediate levels and Rydberg or autoionizing (AI) states in the final ionization step are established. Strong AI resonances were observed via the 3d54s5s f 6S5/2 level at 49 415.35 cm−1, while Rydberg transitions were reached from the 3d54s4d e 6D9/2,7/2,5/2 levels at around 47 210 cm−1. Analyses of the strong Rydberg transitions associated with the 3d54s4d e 6D7/2 lower level indicate that they belong to the dipole-allowed 4d → nf 6F°9/2,7/2,5/2 series converging to the 3d54s 7S3 ground state of Mn II. Fro…
Collisional and thermal ionization of sodium Rydberg atoms III. Experiment and theory fornS andnD states withn= 8–20 in crossed atomic beams
2005
The results of experimental and theoretical studies of collisional ionization of Na Rydberg atoms in nS and nD(n = 8–20) states are presented. Molecular and atomic ions from associative ionization and photoionization by blackbody radiation were detected after pulsed laser excitation of Rydberg states in crossed Na atomic beams. An original method of determination of associative ionization rate constants based on the measurement of ratios of molecular and atomic ion signals was used, which did not require the determination of absolute number density of Rydberg atoms. The measured rate constants of associative ionization of Rydberg atoms in collisions with ground-state Na atoms are compared w…
Untersuchungen von polymeren im massenspektrometer, 6. Poly(oxy-1,4-phenylen), poly(thio-1,4-phenylen) und poly(dithio-1,4-phenylen)
1975
Der thermische Abbau von Poly(oxy-1,4-phenylen), Poly(thio-1,4-phenylen) und Poly(dithio-1,4-phenylen) wurde durch direkte Pyrolyse in der Ionenquelle des Massenspektrometers untersucht. Bei verringerter Elektronenenergie (15 eV) konnten die elektronenstosinduzierten Fragmentierungen der Pyrolysebruchstucke weitgehend zuruckgedrangt und die thermischen Abbaumechanismen ermittelt werden. In Abhangigkeit von den Bruckenatomen werden charakteristische Unterschiede im Abbauverhalten und in der Art der gebildeten Bruchstucke gefunden. Am Beispiel des Poly(dithio-1,4-phenylen)s kann gezeigt werden, das temperaturprogrammierte Pyrolyse und Verwendung eines Datensystems zur Ermittlung von thermisch…
Transition probabilities for BrII lines emitted from a wall-stabilized cascade arc
2000
Abstract Absolute transition probabilities of the eleven Br II lines were measured in emission. A plasma created in a wall-stabilized arc at atmospheric pressure in the mixture of argon and bromine vapors was used as the excitation source. The relative transition probabilities were converted to an absolute scale based on a lifetime value measured by the electron impact method. The results were compared with experimental data. Discrepancies have been found to be outside the experimental uncertainties.